Machine for grinding concrete ceilings



July 24, 1956 s. M. RONVOLD ET AL 2,755,606

MACHINE FOR GRINDING CONCRETE CEILINGS Filed July 14, 1954 k/ t INVENTORS.

WM fy/uw ATTORNEYS.

MACHINE FOR GRIYDING CONCRETE CEILINGS Svend M. Ronvid, Rivei-,Gro ve, and Rudolph T. Stern, Maywood, Ill.

Application .Fuly 14, 1954, Serial No. 443,362. 1 Claim. (Cl. 51-130) This invention relates to a machine for grinding con crete ceilings.

It is the practice to dress. or smooth poured con rete ceilings by grinding. the exposed surfacesjof the ceiling. When this operation is carried out byhand, it is not only tedious for the workman, but it is also difficult to dress the ceiling to a uniformly smooth surface, and the time required is excessive. Therefore, there has been a need for a machine for grinding concrete ceilings, but heretofore no fully satisfactory machine has been developed.

It is frequently desirable to grind concrete ceilings be fore the floor is laid in the building, and this complicates the use of a grinding machine which is adapted to be moved along the floor while grinding the ceiling. When the permanent floor has not been installed, the floor surface will usually be quite uneven. Thus, it is not possible to smooth the ceiling in relation to the floor surface.

it is therefore a general object of this invention to provide a machine for grinding concrete ceilings which overcomes the disadvantages of machines heretofore de veloped for this purpose, and which at the same time is simple to operate and permits the ceiling to be rapidly dressed to a uniformly smooth surface. A more specific object is to provide a machine of the character described which can be operated effectively on uneven floor surfaces and more particularly, in buildings prior to the installation of the permanent floors therein. Still another object is to provide a machine for grinding ceilings which incorporates means for automatically adjusting the grinding head to grind along a horizontal'surface while maintaining pressure on the' ceiling surface. A further object is to provide a machine of the character described which incorporates means for absorbing the shock and vibration of the grinding element against the ceiling so as to prevent or diminish their transfer to the operator of the machine. Still another objectis to provide in a machine for grinding concrete ceilings means for reducing and minimizing the chatter of the grinding element due to unevenness in the ceiling surface being ground or the floor surface upon whichthe machine is resting. Further objects and advantages will appear as the specification proceeds.

This invention is shown in an illustrative embodiment in the accompanying drawing, in which:

Fig. 1 is a perspective view of a machine for grinding concrete ceilings constructed in accordance with this invention; and Fig. 2 is an enlarged detail elevational view of the grinding head and supporting means therefor.

In the embodiment shown in the drawing, the machine comprises generally a movable cart providing an upwardly-extending frame 11, and an operating arm 12 pivotally supported on the upper portion of frame 11 at an intermediate point on arm 12 for movement about a horizontal axis.

More specifically, cart 10 includes a horizontal platform 13 provided with an axle 14 at its front end and having wheels 15 and 16 rotatably carried by the outited States Patent 2 er ends of axle 14. At the rear end of platform 13.;there.

is also provided a caster 17.

Frame 11 includes vertical standards 18, and19; which are similarly braced at theirupper ends by a crossbar 23.

A U-shaped handle bar 24. extends upwardly andv rearwardly from the lower ends of standards 18. and 19, and has its upper end portions secured to crossbarv22; by braces 25 and 26. The horizontal portion- 24a of mem-v ber 24 is adapted to be grasped with the hands for moving cart 16 along the floor. An axle rod 2 7 extends between the upper ends of posts 20 and 21 and is removably at,- tached thereto by pin 28.

In the illustration given, operating arm 12- has a rearwardly-extending portion l2a and a forwardly-extending portion 1212 with reference to the horizonta1:axis,pr ovided by rod 27- on which arm 12' is, pivotally mountedby means of bearing loops 29 and30. Rearwardly-extending arm portion 12a terminates in a handle 31 adapted; to be grasped with the hands for raising and lowering for; weirdly-extending arm porttion 121).

A- support member 32 is pivotally connected to forwardly-extending arm portion 12b on a horizontal axis and forms an angle therewith, as illustrated more clearly in Fig. 2. In the illustration given, support, member 32; is connected to the outer end of forwardly-extendingarm portion 1212 by a strap hinge 33 which has its pin 34;

running parallel to axle rod 27. Preferably as illustrated, supportmember 32 takes the form of a verticallyalignedplate which hasits lower end hingedly connected to the, front end of forwardly-extending arm portion 12b.

For achieving the objects of this invention, it is important that means he provided for maintaining support 32 at the same angle to the horizontal while forwardly; extendingarm portionliZb is raisedandlowered, and that means also be provided for mounting the grinding head of a flexible shaft grinder on support member 32 with the rotational axis of the grinding headin substantially vertical alignment. With this construction the rotational axis of the grinding head will remain vertically aligned. while it is being raised and lowered by operating arm 12, which is important when the. machine is used for grinding ceilings of varying heighths.

Preferably, the means provided for maintainingsup; port member 32 at the same angle to the horizontal while forwardly-extending arm portion 12b is raised and lowered, comprises elements defining a parallelogram in combination with support member 32 and forwardlyextending arm portion 12b and providing pivotal connec tions at the corners of the parallelogram. For example, in the illustration given, sppport member 32 comprises a vertical plate which is hingedly connectedto forwardly extending arm by strap hinge 33, thus defining two sides or" the parallelogram, while the other sides are. definedby rod 35 and strap hinge 36 The outer end. of rod 35 is secured.againstvertical plate.32 by meansof a ball andsocketyconnection at37, which permitsrod 35 to pivot freely with respect to plate 32, and provides the pivotal connection at the outer upper corner of the parallelogram. Strap hinge 36 has its lower leaf vertically aligned and secured to frame 11 by means of attachment plate 38, which in turn is mounted on crossbar 23 and axle rod 27. The inner end of rod 35 is attached to the upper leaf of hinge 36, so that hinge pin 3? provides the pivotal connection at the inner upper corner of the parallelogram. It will be understood that forwardlyextending arm portion 12b and rod 35 should be generally parallel, as are the lower leaf of hinge 36 and the upper leaf of hinge 33. With this arrangement, support plate 32 will remain vertically aligned while it is being raised and lowered by arm 12. To assure that plate 32 is vertically aligned, a turnbuckle 40 can be interposed in rod 35 for making small adjustments in the length of rod 35.

In one phase of this invention, any suitable means can be provided for mounting the grinding head of a flexible shaft grinder on support member 32 with the rotational axis of the grinding head in substantially vertical alignment. However, to fully accomplish the objects of this invention, it is preferred that the mounting means include a compression spring for encircling the upper end of the flexible shaft and resiliently supporting the grinding head. The structure illustrated in the drawing represents a preferred embodiment of this feature of the invention.

The flexible shaft grinder G is shown more fully, in Fig. 1, as including a motor 41 mounted on platform 13, and operated by a switch 42 which is mounted adjacent handle portion 24a. The flexible shaft 43 extends upwardly from motor 41 and has its upper end passed through an opening 44 in mounting plate 45. The grinding head 46 extends above plate 45 with its rotational axis vertically aligned, and includes a grinding element in the form of a cup 47 of abrasive material. Grinding cup 47 is detachably connected to grinding head 46 by means of nut 48. When grinding cup 47 is removed, as is Well known, the outer sleeve 49 of the grinding head can be removed so that the diameter of the grinding head portion is substantially the same as that of flexible shaft 43, thereby permitting the grinding head to be passed through opening 44 in plate 45 even though opening 44 is only of slightly greater diameter than the diameter of shaft 43.

In the illustration given, mounting plate 45 forms a right angle with support plate 32, and thereby lies in a horizontal plane, as illustrated more clearly in Fig. 2. With this relationship between these elements, the rotational axis of the grinding head 46 should be substantially perpendicular to the plane of mounting plate 45, and the mounting head should be supported in such a way as to automatically maintain this alignment. However, it is preferred to support mounting head 46 on a compression spring 56 which encircles the upper end of flexible shaft 43 and resiliently supports the grinding head. More specifically, compression spring 50 is mounted on the top of plate 45 in alignment with opening 44, the bottom end of spring 50 resting on plate 45 and being supported thereby. If desired, a washer 51 can be interposed between the lower end of sleeve 49 and the upper end of spring 50.

Operation In the operation of the grinding machine just described, the elevation of axle rod 27 can be first adjusted by raising or lowering posts 20 and 21 within standards 18 and 19 by shifting adjustment pins 52 in openings 53. After this adjustment has been made, the ceiling can be ground to a uniformly smooth surface in a highly convenient and efiicient manner even though the floor surface is uneven. As already explained, the raising and lowering of the grinding head 46 by means of operating arm 12 will not substantially change the rotational axis of the grinding head, which permits ceilings of varying heighths to be ground without making any adjustment in the elevation of axle rod 27, and at no time will fine adjustments in the elevation of the axle rod be required to cause the grinding surface of cup 47 to run in a substantially horizontal plane. The fine adjustments are taken care of by the resilient supporting of grinding head 46 on compression spring 50. Further, spring 50 also performs the functions of maintaining pressure on the ceiling surface, absorbing vibrations and shock, and reducing chatter. Compression spring 50 will normally be slightly compressed while the grinding operation is being carried out. For example, the operator of the machine will depress handle 31 until grinding cup 47 is forced against the ceiling sufiiciently to compress spring Sit, and this will normally be done after motor 41 has been turned on. The grinding operation can then be carried out by maintaining cup 47 in contact with the ceiling while moving cart 10 over the floor by grasping handle 24a with one hand while the other hand remains on handle 31.

While in the foregoing specification this invention has been described in relation to a specific embodiment thereof and many details have been set forth for purpose of illustration, it will be apparent. to those skilled in the mechanical arts that the invention is susceptible to other embodiments and that many of the details described herein can be varied widely without departing from the basic concepts of the invention.

We claim:

In a machine for grinding concrete ceilings, a movable cart providing an upwardly-extending frame, an operating arm pivotally supported on the upper portion of said frame at an intermediate point on said arm for movement about a horizontal axis, the portion of said arm extending rearwardly from said pivot point being adapted to be grasped with the hands for raising and lowering the forwardly-extending portion of said arm, a vertically-aligned plate member having its lower end portion hingedly connected to the outer end of said forwardlyextending arm portion on a horizontal axis, means linking the upper portion of said plate member to said frame at a point above the intermediate axis of said arm, said linking means being pivotally connected to said plate member and to said frame and running parallel to the forwardlyextending portion of said arm, whereby said plate member remains vertically aligned when said arm is raised and lowered, and a horizontally-aligned plate member carried by said vertically-aligned plate member and having an opening therethrough for loosely receiving the shaft of a flexible shaft grinder, a compression spring having its lower end resting on the top of said horizontally-aligned plate around said opening therein, and means on the upper end of said spring for supporting the grinding head of said flexible shaft grinder when the shaft thereof is positioned within said spring and said opening.

References Cited in the file of this patent UNITED STATES PATENTS 

